The Little Chopper is the chopper commonly sold by the companies that advertise on this forum. It has some adjustment, as has been mentioned, but whether a 5" chopper will go all the way to 4.5" is something I don't know the answer to. I would guess "yes."
There is no guarantee that you will get two 4" feathers out of one full-length feather. Even less guarantee that you will get two 4.5" feathers. I just decided not to worry about it and chop one good feather out of the best part of the full-length feather.
There are better choppers out there than the Little Chopper, but for feathers you find or are given, it might be the best one for you, since it is not so sensitive to quill thickness as the higher quality one is.